The present invention relates to methods for detecting corona discharge and incipient flashover of power line insulators.
Electrical power lines suffer various types of losses. Conductor resistance losses, commonly referred to as I.sup.2 R losses, are often thought to be the major losses. However, electrical leakage of various types at the electrical insulators supporting the power line conductors actually cause losses roughly equivalent to the I.sup.2 R losses. Flashover or catastrophic leakage at an insulator will put the power line out of service.
Bulk electrical conduction through modern power line insulators is negligible. Leakage losses generally occur across the surfaces of the insulators. Such surface conduction depends upon surface film characteristics and local electric field conditions. The electric field conditions depend upon atmospheric conditions, line voltage, insulator geometry, amount of corona and density of ion pairs that happen to be present in the immediate gas layer. Foreign substances which may fall on the insulator surface including chemicals such as nitric acid generated by corona discharge itself, can dramatically reduce surface resistance of such insulators.
As surface resistance of an insulator decreases, the surface conduction increases. The ultimate result is flashover which may result in catastrophic failure of the insulator and shutdown of the power line. Flashover conditions normally do not incur instantaneously but instead develop over a period of time as surface contamination occurs. It would be very desirable to provide means for detecting lower levels of surface contamination and leakage so that corrective actions, such as cleaning the insulator, can be taken before destructive flashover conditions occur.
Accordingly, an object of the present invention is to provide a means for detecting incipient flashover of a power line insulator.
Another object of the present invention is to provide means for increasing conduction conditions on a surface of a power line insulator to a detectable but non-catastrophic level.
According to the present invention, an image intensifier night vision system is used to observe insulators in an energized electrical power line to detect corona discharge, other forms of leakage and elevated insulator temperature indicating excessive electrical leakage.
In one embodiment of the present invention, an ultraviolet laser is used to stimulate surface conduction on power line insulators which do not exhibit abnormal electrical leakage under normal operating conditions, whereby a detectable leakage in response to the laser stimulus indicates low level surface contamination and electrical leakage requiring corrective action.
In another embodiment of the invention, a high frequency, high voltage, electrical pulse is applied to an electrical power line while observing its electrical insulators with an image intensifier to observe any increase in leakage resulting from the high frequency pulse stimulus as an indication of low level leakage requiring corrective action.
In another embodiment of the present invention, the power line voltage is increased momentarily, preferably on a repetitive basis, while observing its electrical insulators with an image intensifier whereby detection of electrical leakage in response to this stimulus indicates a low level leakage requiring corrective action.